Waterborne base coat compositions having a special-effect color

ABSTRACT

A waterborne base coat having a special-effect color and which contains aqueous microgel as binder, 0.5 to 2 wt.-% of poly(meth)acrylic acid thickener and 2 to 7 wt.-% of non-ionically emulsified EVA copolymer wax with a drop point of the wax portion of 80 to 110° C., the wt.-% in each case calculated as solids and relative to the solids content of the waterborne base coat.

FIELD OF THE INVENTION

The invention relates to waterborne base coat compositions (in thefollowing description and the claims also called “waterborne basecoats”) having a special-effect color. The waterborne base coats can beused for the production of the base coat layer in a process for theproduction of a base coat/clear coat two-layer coating having aspecial-effect color on a substrate, in particular on an automotivesubstrate.

DESCRIPTION OF THE PRIOR ART

In the description and the claims the term “special-effect color” isused. A base coat/clear coat two-layer coating with a special-effectcolor is one exhibiting a so-called flop effect. “Flop effect” means thebehavior of a coating to change lightness and/or color dependent on theobservation angle (viewing angle). Said behavior is a result of orientedspecial-effect pigments or flake pigments contained in a coating layerapplied from a correspondingly pigmented coating composition.

Base coat/clear coat two-layer coatings with special-effect colors arewell-known, in particular in automotive coating. Examples include basecoat/clear coat two-layer coatings with a metallic color and/or with amica color.

Accordingly, in the sense of the present invention, a waterborne basecoat with a special-effect color is a waterborne coating compositionfrom which the base coat layer of a base coat/clear coat two-layercoating having a special-effect color can be applied.

Today's automotive coatings generally comprise an electrodepositioncoating (EDC) primer, a primer surfacer layer (filler layer) asintermediate coating layer and a top coat comprising a wet-on-wetapplied color- and/or special effect-imparting base coat layer and aprotective, gloss-imparting clear coat layer (see A. Goldschmidt andH.-J. Streitberger, BASF Handbook on Basics of Coating Technology,Vincentz, Hannover, 2003, pages 702-705).

Waterborne base coats having a special-effect color which containaqueously dispersed microgel particles (hereinafter also called “aqueousmicrogel”) as binder have been disclosed in the patent literature, forexample, in WO 01/72909 A2, WO 2006/118974 A1, EP-A-1 389 627, GB-A-2206 591, US 2003/0220446, US 2003/0204013, US 2006/0128887, US2006/0128859, US 2006/0211813, U.S. Pat. No. 4,403,003, U.S. Pat. No.4,539,363, U.S. Pat. No. 4,945,128, U.S. Pat. No. 5,075,372, U.S. Pat.No. 5,412,023, U.S. Pat. No. 5,977,258, U.S. Pat. No. 6,013,324, U.S.Pat. No. 6,046,259, U.S. Pat. No. 6,538,059 and U.S. Pat. No. 6,770,702.Said microgel particles are organic polymer microparticles which may becomprised of one or more polymer phases, wherein at least one of thepolymer phases is crosslinked. Aqueously dispersed core-shell polymerparticles the core and/or the shell polymer whereof is/are crosslinkedrepresent examples of such multi-phase microgel particles.

SUMMARY OF THE INVENTION

It has now been found that it is possible to improve the appearance(visual impression) of the clear coat layer of base coat/clear coattwo-layer coatings the base coat layer of which has been applied from awaterborne special-effect color base coat containing aqueous microgelbinder. The improvement in appearance, in particular an improved glossof the clear coat layer can be obtained when such waterborne base coatcontains a specific additive combination of poly(meth)acrylic acidthickener and non-ionically emulsified EVA (ethylene/vinyl acetate)copolymer wax with a drop point of the wax portion of 80 to 110° C. Theimproved appearance of the finished clear coat layer can visually beperceived; however, it can also be determined as a minimized short wave(SW) and/or minimized dullness (du, Wa, Wb) of the clear coat surfacestructure. The SW and dullness can be determined with the measuringdevice Wavescan DOI from BYK-Gardner.

The term “(meth)acryl” used herein means methacryl and/or acryl. In thedescription and the claims the term “drop point” (also called “droppingpoint”) is used. Drop point and melting point shall not be confused witheach other, although both temperature points describe the same or almostthe same, namely the temperature at which a material passes from a solidor semi-solid state into the liquid state. Melting point and drop pointmeasurements of a material may lead to the same result; however, thedrop point may also be slightly higher or slightly lower than themelting point. The drop point is determined according to DIN ISO 2176(May 1997).

The invention is directed to waterborne base coats having aspecial-effect color and which contain aqueous microgel as binder, 0.5to 2 wt.-% (weight-%) of poly(meth)acrylic acid thickener and 2 to 7wt.-% of non-ionically emulsified EVA copolymer wax with a drop point ofthe wax portion of 80 to 110° C., the wt.-% in each case calculated assolids and relative to the solids content (overall solids) of thewaterborne base coats.

The invention is also related to a process for the formation of a basecoat/clear coat two-layer coating having a special-effect color on asubstrate, wherein the base coat layer is applied from a waterborne basecoat of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The waterborne base coats of the present invention are aqueous coatingcompositions having a solids content of 15 to 25 wt.-%. In addition towater, a resin solids content comprising the aqueous microgel binder, apigment content, the poly(meth)acrylic acid thickener and thenon-ionically emulsified EVA copolymer wax, the waterborne base coatsmay contain one or more of the following optional components: fillers(extenders), organic solvents, additives other than (otherthan=different from) poly(meth)acrylic acid thickeners and also otherthan non-ionically emulsified EVA copolymer waxes. The waterborne basecoats have a ratio by weight of pigment content to resin solids contentof, for example, 0.08:1 to 0.6:1.

The term “solids content” used in the present description and the claimsmeans the sum of the non-volatile components of a coating composition,i.e. the sum of the resin solids, pigments, fillers and non-volatileadditives. The rest of the coating composition is formed by volatilecomponents, i.e. water, optionally present organic solvents andoptionally present volatile additives.

The term “resin solids content” used in the present description and theclaims means the sum of the solids contributions of the coating binders(binder solids) and the solids contributions of crosslinkers(crosslinker solids, crosslinking agent solids) optionally contained ina coating composition. The coating binders comprise the aqueous microgelbinder (calculated without water) and they include paste resinsoptionally contained in the coating composition.

The term “pigment content” used in the present description and theclaims means the sum of all the pigments contained in a coatingcomposition. The pigment content does not comprise fillers. The term“pigments” is used here as in DIN 55944 (November 2003) and covers, inaddition to special-effect pigments, inorganic white, colored and blackpigments and organic colored and black pigments. At the same time,therefore, DIN 55944 distinguishes between pigments and fillers.

The waterborne base coats of the present invention contain anionicallyand/or non-ionically stabilized aqueous binder systems. Anionicstabilization is preferably achieved by at least partially neutralizedcarboxyl groups in the binder, while non-ionic stabilization ispreferably achieved by lateral and/or terminal polyethylene oxide units(polyethylene glycol structures) in the binder. The waterborne basecoats may be physically drying or crosslinkable by formation of covalentbonds. The crosslinkable waterborne base coats forming covalent bondsmay be self- or externally crosslinkable systems.

The waterborne base coats of the present invention contain one or moreconventional water-dilutable film-forming binders, wherein at least oneof said binders is an aqueous microgel. The aqueous microgel iscontained in the waterborne base coats in a proportion of, for example,20 to 70 wt.-% of the binder solids. In an embodiment, the proportion ofaqueous microgel is 20 to 50 wt.-% of the binder solids.

Suitable aqueous microgels that can be used to form the waterborne basecoats of the present invention include those disclosed in the patentliterature cited in the section “Description of the Prior Art”. Themicrogel preferably contains appropriate functional groups, such ashydroxyl groups, whereby they can become crosslinked, after applicationof the waterborne base coat, by means of a crosslinking agent.

The aqueous microgels may be composed of various types of crosslinkedpolymers. Of particular interest for the purposes of this invention arecrosslinked (meth)acrylic microgel particles. Preparation of such(meth)acrylic microgels may be carried out by methods that are wellknown and routinely practiced by those of ordinary skill in the art.Typically, the microgels are (meth)acrylic addition polymers mainlyderived from one or more alkyl (meth)acrylates, optionally together withother ethylenically unsaturated copolymerizable monomers like styreneand vinyl esters. Suitable alkyl (meth)acrylates include, withoutlimitation, alkyl (meth)acrylates each having 1-18 carbon atoms in thealkyl group. Since the (meth)acrylic microgel is required to be formedwith internal crosslinking, there may be included in the monomers fromwhich the (meth)acrylic microgel is derived a minor proportion of amonomer which is polyfunctional with respect to the polymerizationreaction, such as ethylene glycol di(meth)acrylate, allyl (meth)acrylateor divinylbenzene.

Alternatively, there may be included in the monomers minor proportionsof two other monomers carrying pairs of functional groups which can becaused to react with one another either during or after polymerization,such as epoxy and carboxyl (as for example, in glycidyl methacrylate and(meth)acrylic acid), anhydride and hydroxyl, or isocyanate and hydroxyl.There also is preferably included in the monomers from which the(meth)acrylic microgel is derived minor amounts of a hydroxyl containingmonomer for crosslinking purposes after application of the waterbornebase coat, for example, a hydroxy alkyl (meth)acrylate.

Acid functional monomers such as (meth)acrylic acid are also preferablyincluded in the monomer mix to anionically stabilize the (meth)acrylicmicrogels in the aqueous base coat by converting such groups to asuitable salt by reaction with a base, such as dimethylaminoethanol.Stability in aqueous base coat can also be achieved through the use ofsurfactants or macromonomers that contain water-soluble nonionicstabilizers such as materials that contain polyethylene glycolstructures.

In addition to the aqueous microgel, the waterborne base coats of thepresent invention contain at least one water-dilutable “non-microgel”binder. Examples of suitable binders are conventional water-dilutablebinders familiar to the person skilled in the art, such aswater-dilutable polyester resins, water-dilutable (meth)acryliccopolymer resins, water-dilutable polyester/(meth)acrylic copolymerhybrids, water-dilutable polyurethane resins and water-dilutablepolyurethane/(meth)acrylic copolymer hybrids.

The waterborne base coats of the present invention may optionally alsocontain crosslinking agents if the binders are not self-crosslinkable orphysically drying. Selection of the optionally contained crosslinkingagents depends, in a manner familiar to the person skilled in the art,on the functionality of the binders, i.e., the crosslinking agents areselected in such a way that they exhibit a reactive functionalitycomplementary to the functionality of the binders. Examples of suchcomplementary functionalities between binder and crosslinking agent are:carboxyl/epoxy, hydroxyl/methylol ether and/or methylol (methylol etherand/or methylol preferably, as crosslinkable groups of amino resins, inparticular, melamine resins). Examples of crosslinking agents includefree or blocked polyisocyanates and amino resins, for example, melamineresins. The crosslinking agents may be used individually or incombination. The weight ratio between crosslinking agent solids andbinder solids amounts, for example, to 10:90 to 40:60.

As already mentioned, the waterborne base coats of the present inventionhave special-effect colors. Accordingly, they comprise an appropriateamount of at least one special-effect pigment; the solids contents ofthe waterborne base coats comprise, for example, 8 to 25 wt.-% of one ormore special-effect pigments. Examples of special-effect pigments arethose flake pigments or platelet pigments imparting to a coating aviewing angle-dependent color and/or lightness flop, such as,non-leafing metal pigments like in particular, aluminum flake pigments,interference pigments, such as, e.g., metal oxide-coated metal pigments,e.g., iron oxide-coated aluminum, coated micas, such as, e.g., titaniumdioxide-coated mica, pigments producing a graphite effect,platelet-shaped iron oxide, liquid crystal pigments, coated aluminumoxide pigments and coated silicon dioxide pigments.

In addition to the at least one special-effect pigment the pigmentcontent of the waterborne base coats of the present invention cancomprise one or more pigments other than the at least one special-effectpigment. Examples of pigments other than the at least one special-effectpigment are conventional pigments selected from white, colored and blackpigments, such as, e.g., conventional inorganic or organic pigmentsknown to the skilled person, for example, titanium dioxide, iron oxidepigments, carbon black, azo pigments, phthalocyanine pigments,quinacridone pigments, pyrrolopyrrol pigments and perylene pigments.

The waterborne base coats of the present invention may also containfillers, for example, in proportions of 0 to 25 wt.-% relative to theresin solids content of the waterborne base coats. The fillers do notconstitute part of the pigment content of the waterborne base coats.Examples of fillers are barium sulfate, kaolin, talcum, silicon dioxide,layered silicates and any mixtures thereof.

The special-effect pigments present in the waterborne base coats of thepresent invention are generally initially introduced in the form of aconventional commercial aqueous or non-aqueous paste, optionally,combined with preferably water-dilutable organic solvents and additivesand then mixed with aqueous binder. Pulverulent special-effect pigmentsmay first be processed with preferably water-dilutable organic solventsand additives to yield a paste.

White, colored and black pigments and/or fillers may, for example, beground in a proportion of the aqueous binder. Grinding may preferablyalso take place in a special water-dilutable paste resin. Grinding maybe performed in conventional assemblies known to the person skilled inthe art. The formulation is then made up with the remaining proportionof the aqueous binder or of the aqueous paste resin.

The waterborne base coats of the present invention containpoly(meth)acrylic acid thickener in a proportion of 0.5 to 2 wt.-%,calculated as solids and relative to the solids content of thewaterborne base coats. Poly(meth)acrylic acid thickeners are thickenersknown to the person skilled in the art of aqueous paint and coating, forexample, copolymers of (meth)acrylic acid and (meth)acrylic acid esterscontaining polymerized (meth)acrylic acid, for example, in an amount of30 to 60 by weight. Viscalex® HV 30 from Ciba is an example of acommercially available poly(meth)acrylic acid thickener. Thepoly(meth)acrylic acid thickeners are used in an at least partiallyneutralized form in the waterborne base coats, or, after their additionto the waterborne base coats, are at least partially neutralized. Aminesor aminoalcohols are particular examples of alkaline neutralizing agentswhich can be used for partially or totally neutralizing thepoly(meth)acrylic acid thickeners.

The waterborne base coats of the present invention contain non-ionicallyemulsified EVA copolymer wax with a drop point of the wax portion of 80to 110° C. in a proportion of 2 to 7 wt.-%, calculated as solids andrelative to the solids content of the waterborne base coats. To avoidmisunderstandings, the 2 to 7 wt.-% include the solids contribution ofthe non-ionic emulsifier or non-ionic surfactant. The EVA copolymerwaxes having a drop point of 80 to 110° C. contain, in particular, 6 to14 wt.-% of copolymerized vinyl acetate. The weight ratio betweennon-ionic emulsifier or non-ionic surfactant and the EVA copolymer waxof the non-ionically emulsified EVA copolymer wax is, for example,0.1:99.9 to 10:90, or, in an embodiment, for example, 0.5:99.5 to 5:95.

The poly(meth)acrylic acid thickener and the non-ionically emulsifiedEVA copolymer wax with a drop point of the wax portion of 80 to 110° C.may be introduced into the waterborne base coats of the presentinvention as separate components and/or in the form of an intermediateproduct containing both additives in combination. Aquatix® 8421 from BYKis an example of such a commercially available intermediate product.

In addition to the poly(meth)acrylic acid thickener and thenon-ionically emulsified EVA copolymer wax with a drop point of the waxportion of 80 to 110° C., the waterborne base coats of the presentinvention may contain conventional paint additives other thanpoly(meth)acrylic acid thickeners and other than non-ionicallyemulsified EVA copolymer waxes. Such conventional paint additives may becontained in conventional quantities, for example, of 0.1 to 5 wt.-%,relative to the solids content of the waterborne base coats. Examples ofsuch conventional paint additives include neutralizing agents,antifoaming agents, wetting agents, adhesion promoters, catalysts,levelling agents, anticratering agents and thickeners other thanpoly(meth)acrylic acid thickeners.

The waterborne base coats of the present invention may containconventional organic solvents, for example, in a proportion ofpreferably less than 25 wt.-%, particularly preferably less than 20wt.-%, based on total waterborne base coat. Examples of such organicsolvents are alcohols, for example, propanol, butanol, hexanol; glycolethers or esters, for example, diethylene glycol di-C1-C6-alkyl ether,dipropylene glycol di-C1-C6-alkyl ether, ethoxypropanol, ethylene glycolmonobutyl ether; glycols, for example, ethylene glycol and/or propyleneglycol, and the di- or trimers thereof; N-alkylpyrrolidone, such as, forexample, N-ethylpyrrolidone; ketones such as methyl ethyl ketone,acetone, cyclohexanone; aromatic or aliphatic hydrocarbons, for example,toluene, xylene or linear or branched aliphatic C6-C12 hydrocarbons.

The waterborne base coats of the present invention can be used tospray-apply the base coat layer of base coat/clear coat two-layercoatings having special-effect colors.

The invention is therefore also related to a process for the productionof a base coat/clear coat two-layer coating having a special-effectcolor, wherein the base coat layer is spray-applied from a waterbornebase coat of the present invention onto a substrate. The processcomprises the steps:

-   (1) providing a substrate to be provided with a base coat/clear coat    two-layer coating having a special-effect color,-   (2) spray-applying a waterborne base coat of the present invention    on the substrate to form the base coat layer,-   (3) spray-applying a clear coat composition on the base coat layer    formed in step (2) to form the clear coat layer, and-   (4) jointly curing the base coat layer and the clear coat layer at    an object temperature at or above the drop point of the wax portion    of the non-ionically emulsified EVA copolymer wax having a drop    point of 80 to 110° C.

The substrate provided in process step (1) can be a plastics or a metalsubstrate. Plastics substrates may have a precoating like a conductiveprimer layer; metal substrates may have a precoating like a conventionalEDC primer layer and, optionally, also a conventional primer surfacerlayer. Examples of substrates include in particular automotive bodiesand body parts, which typically have a suitable precoating. Automotivebodies may in particular have a precoating consisting of a conventionalEDC primer layer or of a conventional EDC primer layer plus aconventional primer surfacer layer. Automotive body metal parts may inparticular have a precoating consisting of a conventional EDC primerlayer or of a conventional EDC primer layer plus a conventional primersurfacer layer, whereas automotive body plastics parts may in particularhave a precoating consisting of a conductive primer layer.

The substrate provided in process step (1) is provided with a basecoat/clear coat two-layer coating having a special-effect color bycarrying out the wet-on-wet coating process comprising process steps (2)to (4) in the course of which the base coat layer and the clear coatlayer both are applied and jointly cured.

In process step (2) the (precoated) substrate is spray-coated with awaterborne base coat of the present invention. Application of thewaterborne base coat may be performed by any known spray-applicationmethod like, for example, pneumatic spray-application orelectrostatically-assisted high-speed rotary atomization. In anembodiment, the spray-application is performed in two spray passes (twosubsequent spray operations), the first of which being performed byelectrostatically-assisted high-speed rotary atomization and the secondby pneumatic spray-application. In a preferred embodiment, thespray-application is performed only by electrostatically-assistedhigh-speed rotary atomization, which may be performed in two spraypasses or even in one single spray pass.

The waterborne base coat is applied in a total dry film thickness of,for example, 7 to 22 μm.

The applied base coat layer is preferably briefly flashed off beforeprocess step (3) is performed. The flash-off phase takes, for example,30 seconds to 10 minutes at an air temperature of 20 to 80° C.

In process step (3), a clear coat composition is spray-applied on thenot yet fully cured or even uncured base coat layer formed in processstep (2). Application of the clear coat may be performed by any knownspray-application method like, for example, pneumatic spray-applicationor electrostatically-assisted high-speed rotary atomization, the latterspray-application method being the preferred one. The clear coatcomposition is applied in a total dry film thickness of, for example, 30to 60 μm.

All known clear coat compositions are in principle suitable. Usableclear coats are here both solvent-containing one-component (1 pack) ortwo-component (2 pack) clear coats and water-dilutable 1 pack or 2 packclear coats.

After an optional, but preferred flash-off phase the applied base coatlayer and the clear coat layer are jointly cured in process step (4).The joint curing is performed at an object temperature at or above thedrop point of the wax portion of the non-ionically emulsified EVAcopolymer wax having a drop point of 80 to 110° C. The objecttemperature is, for example, 80 to 160° C., in particular, 120 to 160°C., and the joint curing is carried out, for example, by baking.

EXAMPLES Example 1 Preparation of an Aqueous Binder Latex

A reactor was charged with 688 pbw (parts by weight) of deionized waterand 16 pbw of Rhodapex EST30 (anionic surfactant available from Rhodia;30 wt. % in water). The water and surfactant charge was heated to 80° C.under nitrogen atmosphere and held at that temperature throughout thereaction. A first stirred monomer emulsion consisting of 45 pbw ofRhodapex EST30, 349 pbw of deionized water, 270 pbw of methylmethacrylate, 189 pbw of butyl acrylate, 175 pbw of styrene, 36 pbw ofhydroxyethyl acrylate, 36 bpw of methacrylic acid and 7 pbw of allylmethacrylate was prepared separately. A solution of 3.2 pbw of ammoniumperoxodisulfate (APS) in 100 pbw of deionized water was added to thereactor content and the first monomer emulsion was then added within 90minutes to the reactor content. After all of the first monomer emulsionwas in, the reactor content was held for an additional hour at 80° C.,during which a second stirred monomer emulsion consisting of 15 pbw ofRhodapex EST30, 378 pbw of deionized water, 277 pbw of methylmethacrylate, 180 pbw of butyl acrylate, 175 pbw of styrene, 72 pbw ofglycidyl methacrylate and 7 pbw of allyl methacrylate and a solution of13 pbw of 2-amino-2-methyl-1-propanol (90 wt. % in water) in 98 pbw ofdeionized water were separately prepared. The aqueous2-amino-2-methyl-1-propanol solution was added slowly to the reactionmixture and then, a solution of 1.1 pbw of ammonium peroxodisulfate(APS) in 70 pbw of deionized water was added slowly to the reactorcontent. The second monomer emulsion was then added within 90 minutes tothe reactor content. After the addition was complete, the reactorcontent was held at 80° C. for an additional hour. The aqueous binderlatex obtained was then cooled to room temperature.

Example 2 Preparation of an Aqueous Polyurethane Binder Dispersion

1005 g of a straight-chain polyester (composed of adipic acid,isophthalic acid and hexanediol having a hydroxyl value of 102 mg KOH/g)were heated to 90° C. and 1.8 g of trimethylolpropane and 393 g ofisophorone diisocyanate were added. The reaction was carried out at 90°C. until the NCO value was constant. After cooling to 60° C., a solutionof 35.3 g of dimethylol propionic acid, 26.1 g triethylamine and 250 gN-ethylpyrrolidone was added. After heating to 80° C., the reactiontemperature was maintained until the NCO value was constant. The batchwas mixed with a molar amount, based on the molar NCO-content, ofdeionized water, and the solution was kept at 80° C., until no more NCOwas detectable. The batch was then converted into an aqueous dispersionhaving a solids content of 35 wt. % by adding deionized water.

Examples 3a to 3b Preparation of Waterborne Metallic Base Coats

Waterborne metallic base coats 3a to 3b were prepared by mixing theconstituents listed in Table 1. Proportions are in pbw. Table 1 alsoshows dullness data of multi-layer coatings prepared with the waterbornebase coats.

TABLE 1 Silver-metallic waterborne base coats 3a **⁾ 3b *⁾ Constituents:BE 2.5 2.5 Aluminum paste ¹⁾ 15 15 NEP 1 1 Binder dispersion of Example2 13 13 Deionized water 15 10 Aqueous binder latex of Example 1 10 10Deionized water 15 10 Layered silicate composition ²⁾ 0 17 Maprenal ® MF900 ³⁾ 3 3 Cymel ® 325 ⁴⁾ 2 2 Deionized water 12.4 8.9 Thickener ⁵⁾ 0 3Aquatix ® 8421 5 0 DMEA, 10 wt. % solution in water 3.5 2 BuOH 2.6 2.6Dullness ⁶⁾ 23 33 Wa ⁶⁾ 18 27 Wb ⁶⁾ 22 24 *⁾ comparative example **⁾according to the invention BE, Butoxy ethanol BuOH, n-Butanol DMEA,Dimethylethanolamine NEP, N-Ethyl pyrrolidone ¹⁾ Mixture of 50 pbw BEwith 50 pbw Stapa Hydrolan ® IL 2156 from Eckart. ²⁾ Mixture of 3 pbwLaponite ® RD from Rockwood Additives Ltd., 3 pbw polypropylene glycol900 and 94 pbw of deionized water. ³⁾ Melamine resin from SurfaceSpecialties. ⁴⁾ Melamine resin from Cytec. ⁵⁾ Mixture of 33 pbw ViscalexHV 30 from Allied Colloids, 2.5 pbw DMEA and 64.5 pbw of deionizedwater. ⁶⁾ The water-borne base coats were each applied byelectrostatically-assisted high-speed rotary atomization in one singlespray pass to steel test panels provided with a precoating consisting ofEDC primer and primer surfacer in 12 μm dry film thickness. Afterflashing-off for 5 minutes at 20° C. and additional 5 minutes at 80° C.the test panels were each spray coated with a commercial two-componentpolyurethane clear coat in 40 μm dry film thickness and afterflashing-off for 5 minutes at 20° C. baked for 20 minutes at 140° C.object temperature. Dullness, Wa and Wb values were determined on theclear coat surface with the measuring device Wavescan DOI fromBYK-Gardner.

1. A waterborne base coat having a special-effect color and whichcontains aqueous microgel as binder, 0.5 to 2 wt.-% of poly(meth)acrylicacid thickener and 2 to 7 wt.-% of non-ionically emulsified EVAcopolymer wax with a drop point of the wax portion of 80 to 110° C., thewt.-% in each case calculated as solids and relative to the solidscontent of the waterborne base coat.
 2. The waterborne base coat ofclaim 1, wherein the aqueous microgel totals 20 to 70 wt.-% of thebinder solids of the waterborne base coat.
 3. The waterborne base coatof claim 1, wherein the aqueous microgel totals 20 to 50 wt.-% of thebinder solids of the waterborne base coat.
 4. The waterborne base coatof claim 1, wherein the EVA copolymer wax having a drop point of 80 to110° C. contains 6 to 14 wt.-% of copolymerized vinyl acetate.
 5. Thewaterborne base coat of claim 1 containing a crosslinking agent selectedfrom the group consisting of free polyisocyanates, blockedpolyisocyanates, amino resins and any combinations thereof.
 6. A processfor the production of a base coat/clear coat two-layer coating having aspecial-effect color comprising the steps: (1) providing a substrate tobe provided with a base coat/clear coat two-layer coating having aspecial-effect color, (2) spray-applying a waterborne base coat of anyone of the preceding claims on the substrate to form the base coatlayer, (3) spray-applying a clear coat composition on the base coatlayer formed in step (2) to form the clear coat layer, and (4) jointlycuring the base coat layer and the clear coat layer at an objecttemperature at or above the drop point of the wax portion of thenon-ionically emulsified EVA copolymer wax having a drop point of 80 to110° C.
 7. The process of claim 6, wherein the substrate is selectedfrom the group consisting of uncoated plastics substrates, precoatedplastics substrates, uncoated metal substrates and precoated metalsubstrates.
 8. The process of claim 6, wherein the substrate is selectedfrom the group consisting of automotive bodies and body parts.
 9. Theprocess of any one of claim 6, wherein the spray-application of thewaterborne base coat is performed by a spray-application method selectedfrom the group consisting of (i) two spray passes (two subsequent sprayoperations), the first of which being performed byelectrostatically-assisted high-speed rotary atomization and the secondby pneumatic spray-application, (ii) electrostatically-assistedhigh-speed rotary atomization performed in one single spray pass and(iii) electrostatically-assisted high-speed rotary atomization performedin two spray passes.